1. Technical Field
The present invention relates to air springs and in particular to the piston member thereof. The piston is formed of a plastic material and has two separate internal air reservoirs to increase the air volume within the air spring and has a minimal support surface for mounting the air spring on a supporting structure.
2. Background Information
Air actuators and in particular air springs, consist of a pair of spaced end members and an intervening flexible sleeve or bellows which forms an internal pressurized fluid chamber. These devices are used for many applications, such as mounting between spaced components of a vehicle for absorbing road shock, supporting parts of machines and equipment, such as presses on which shock forces are continually imparted, and for regulating and maintaining the spacing between two spaced components of various types of equipment. These air springs assume various configurations depending upon their particular applications. Such air springs usually consist of an end member such as an end cap, with an other end member being a piston. The piston will have a designed outer surface over which a rolling lobe of the flexible sleeve moves for affecting the damping of the vehicle or equipment on which the air spring is mounted. Prior art air springs and in particular the pistons thereof, are usually fabricated from steel thereby increasing weight, cost and presenting corrosion problems. Also, it is desirable to increase the internal volume or air space within the air spring without materially increasing the size of the air spring to provide greater flexibility in achieving ride softness by effecting the rate of the air spring as well as lowering the natural frequency which will improve the air spring vibration isolation capability.
Another problem with existing air springs is that the bottom of the piston requires a large surface area for mounting on one of the spaced components of a vehicle or equipment, which space is not readily available or is unattainable for certain applications.
U.S. Pat. No. 4,564,177 describes an air spring having a plastic piston which provides a very small upper hollow portion functioning as an auxiliary reservoir. However, the piston requires a large surface area for mounting it on the supporting structure.
U.S. Pat. No. 4,650,166 discloses a two-piece piston which forms an auxiliary reservoir but requires a full sized base for supporting the piston on a support structure.
U.S. Pat. No. 4,787,606 discloses a plastic piston for an air spring formed of two separate members which when connected together form two chambers, but the chambers are not utilized as auxiliary reservoir chambers for receiving pressurized air. Likewise, the mounting base extends throughout the entire width of the piston.
U.S. Pat. No. 4,890,823 is believed to be the most pertinent piston to the subject invention in that it discloses a two-piece plastic piston. However, the base is not utilized to form the auxiliary reservoir as is that of the present invention, and the lower mounting surface or base is equal to the entire circumference of the piston base.
U.S. Pat. No. 5,326,082 discloses a plastic piston having an auxiliary reservoir in the central portion thereof. However, it requires a large mounting surface or base for mounting the piston on a support structure.
U.S. Pat. No. 5,342,139 discloses a plastic piston which again requires a large mounting base or surface for supporting the piston on a vehicle component.
U.S. Pat. No. 5,382,006 discloses a piston formed of metal which does provide an auxiliary reservoir. However, the mounting surface of the piston base extends completely throughout the circumference of the piston, and thus requires a large mounting surface on the supporting structure.
U.S. Pat. No. 5,707,045 discloses a plastic piston for an air spring having an auxiliary reservoir. Again, the supporting area of the base extends throughout the entire circumference of the piston.
U.S. Pat. No. 5,752,692 discloses a plastic piston having a hollow interior which forms an auxiliary reservoir with the pressure chamber of the bellows. However, the piston is mounted on an air strut and thus is not concerned with a base for mounting it on a supporting structure such as on a vehicle.
The present invention provides a piston for an air spring which is formed of a lightweight, high strength plastic material which enables the internal volume of the air spring to be increased considerably without materially affecting the size of the air spring to affect the rate of the air spring, thereby lowering its natural frequency to improve its vibration isolation capability.
The air spring piston of the invention is provided with a pair of internal subchambers connected by fluid passageways, which subchambers communicate fluidly with the main fluid chamber of the flexible sleeve, without sacrificing the structural integrity and strength of the piston by providing a plurality of radially extending reinforcing ribs within both of the subchambers.
Another aspect of the invention provides a reduced central base area which provides an outwardly extending end surface or pedestal in order to support the air spring assembly on a relatively small surface area.
Another feature of the invention is forming the piston of a thermoplastic material which reduces the weight and cost, yet which provides increased internal volume and reduced mounting surface area.
A further feature of the invention is forming the air spring piston of two components, a main shell and a separate base, which components can be easily joined using readily available welding techniques, adhesives or various fastening devices.
Another aspect of the invention is to provide a variety of internal strengthening ribs to enable the piston to withstand the application loads and pressure without materially increasing the size and weight of the piston.
The foregoing advantages, construction and operation of the present invention will become more readily apparent from the following description and accompanying drawings.